Automatic telephone system



March 2 ,1926. 1,575,602

W. T. POWELL 'AUTOMA'TIC TELEPHONE SYSTEM Filed April 5, 1922 5Sheets-Sheet l PRIMARY LINE SWITCH.

RELAY 42' MAGNETIS RELAY :2

RELAY H RELAYIE TESTING auaY TRUNK.

24 vow;

RESISTANCE 2E INVENTOR WIHFRED T. POWELL.

AlWg ATTORNEY March 2 1926.

W. T. POWELL AUTOMATIC TELEPHONE SYSTEM 5 Sheets-Sheet 2 Filed Aoril 5,1922 March 2 1926.

w. T. POWELL AUTOMATI C TELEPHONE SYSTEM 5 Sheets-Sheet 5 Filed April 3,1922 INVENTOR WINFRED w: POWELL.

BY A. ATTORNEY March 2 1926. 1,575,602

7 w. "r. POWELL AUTOMATIC TELEPHONE SYSTEM Filed April 5. 9 5Sheets-Sheet 4 TNs REGISTER.

INVENTOR WIHFRED T POWELL BY AZ [W ATTORNEY March 2 1926.

W. T. POWELL AUTOMATIC TELEPHONE SYSTEM Filed April 5, 192?5Sheets-Sheet 5 WIN WINFRED T. POWELL ATTORNEY EOPUMZZOO Patented Mar.2, 1926.

UNITED TATES ATENT OFFICE.

WINFRED T. POWELL, OF ROCHESTER, NEW YORK, ASSIGNOR TO THE STROMBERG-OARLSON TELEPHONE MANUFAOTURING COMPANY, OF ROCHESTER, NEW YORK,

A CORPORATION OF NEW YORK.

Application filed April 3, 1922. Serial No. 548,943.

'1 0 all whom it may concern Be it known that I, VVINFRED T. POWELL, acitizen of the United States, residing at Rochester, in the county ofMonroe and State of New York, have invented certain new and usefulImprovements in Automatic Telephone Systems, of which the following is afull, clear, concise, and exact description.

This invention relates to telephone systems and more particularly totelephone systems employing automatic switches in completing someportion of a telephone connection.

This invention has for its purpose the provision of novel testing meansfor a trunk hunting switchby which such switch may test a plurality oftrunks, indicated as lousy trunks and finally seize an idle trunk andhold the trunk thus seized.

Various features of the invention will appear in the course of thefollowing description and the appended claims.

In the drawings Figs. 1, 2, 3 and 4 diagrammatically represent one formof telephone system incorporating the present invention, in which attheleft of Fig. 1 there are represented substations and lines of twosubscribers which terminate in a single primary line switch the brushesof which appear near the center of Fig. 1. In Fig. 2

there is represented the operating circuits of an odd secondary lineswitch shown above the dotted line, and below this line there isrepresented the operating circuits of an even secondary line switch. Inthe lower right hand corner of Fig. 3 there is represented the operatingcircuits of a register selector which functions to select an idleregister sender and connect the same to a bridge circuit to which thecalling line is connected. The remainder of this figure represents whatmay be termed, a bridge circuit over which a conversational circuit isfinally eon'ipleted. In the lower left'hand corner of Fig. 4, there isshown a group of five test relays which may be common to one hundredlines. Near the center portion. of Fig. 4 there appears the operatingcircuits of the tens register, while at the extreme right of this figurethere appears the units register. Fig. 5 is a diagram showing conditionswhich exist during the testing of a busy trunk.

In Fig. 6 there is represented a modified form of the invention, whilein Figs. 7 and 8 there is diagrammatically represented theconditionwhich exists when the line switch of Fig. 6 tests-a busy trunkand also when this line switch tests an idle trunk.

The mechanical structure of the switches employed in this system may besubstantially similar to that disclosed in the patent to Clement#1,107,153 granted August '11, 1914:, while the multi-contact relaysmaybe similar to the structure of such relays which are now well known.j

l/Vith this brief description of the ap paratus, it is believed thatthe'invention will best be understood by describing the method ofestablishing a telephone connection from a substation such as isindicated at A, to a substation which is indicated at B.

hen the subscriber at A removes his receiver from its switch hook, acircuit is completed for the line relay '10, extending from groundedbattery, winding of this relay, uppermost back contact andrarmature ofcutoff relay 11, over the lower side of the calling line and through thesubstation circuits in series, over the upper side of the calling line,upper armature and back contact of the cut off relay 12 to ground. Theline relay is energized in this circuit and attracts its armatures,thereby completing an operating circuit for the motor magnet 13extending from grounded battery, resistance 22, inner armature and frontcontact of line relay 10, winding of the motor 1nagnet'13, its backcontact and armature, lowermost front contact. and armature of linerelay 10, inner upper armature and back contact of cutoff relay 11 toground. trol of this circuit the motor magnet 13 advances the brushes1%, 15, 16, 17, 18 and 19 of the primary line switch until its testbrush 16 engages an idle test terminal such as 20. V This idle conditionis indicated by the presencevof ground potential on the test terminal 20which is applied through the back contact and armature of a relay suchas 23, over test conductor 24. In the event that the first trunk testedis busy, its test Under the con 1 terminal similar to 20 ischaracterized -by the presence of battery potential thereon, appliedthrough resistance 21, front contact and armature of relay 23, testconductor 24 -tery, resistance to the testterminal 20. The applicationof battery potential to this test terminal results in the inclusion ofthe energizing winding of the cut-off relays such as 11 and 12 of theline switch of Fig. 1 in the neutral branch of the lVheatstone bridgewith the result that these relays are not operated and the motor magnet13 continues to advance the primary line switch brushes until the idletrunk is located.

This condition is diagrammatically represented in Fig. 5 wherein-theresistance values of the different resistances and windings of therelays and-magnets are given. This dia gram indicates-that when a trunkis seized, a circuit is closed from the battery through resistance21,-test terminal test brush 16 of the line switch that has alreadyseized thistrunk through the low resistance windings of the cut-offrelays 12 and 1-1 associated with that line switch and through the highresistance windings in multiple of the cut-off relays 11 and 12associated with that switch, to ground, also at the time of this testanother circuit closed from the hat- 22, and through the winding of themotor magnet 13 toground. It will thus beseen that the ratio arms ofithelVheatstone bridge are of such resistance values that sufficient currentdoes not pass through the low resistance windings of the cut-elf relays11 and 12, test brush 16 and multiple terminal 20, to operate these lastmentioned relays. At this time a circuit is completed from ground, backcontact and armature of relay 23, test conductor 2 1, test terminal20,-test brush 16, upper. low resistance winding of cut-off relay 12,the lower winding of cut-01f relay 11 which is of low resistance,conductor 25, inner front contact and armature of line relay 10,resistance 22, to grounded battery.

The cut-off relays 11 and 12 are energized inthis circuit and thecalling line is extended through the uppermost arn'iatures and frontcontacts of relays 11and 12 to the line switch brushes 151 and '15 andthence to ground through armature 2 and back contact of relay 27 andthrough the armature 28 and back contact of relay 27 and the winding ofrelay 29rto grounded battery. The relay 29 is energized in this circuitand mmediately operates the relay 23 over a circuit traceable fromgrounded battery, winding of this relay, lowermost front contact andarmature of relay 29 to ground. ll ith the relay 23 tact and armature ofthis relay to ground which holds relay 11 operated. multiple of that)ust described includes the A circuit in lower winding of relay l1,conductor 115,

lower winding of cutolf relay l2, conductor 116, inner upper frontcontact and armature of relay 1.1 to ground. This circuit maintainsrelay 12 operated.

It should benoted that during the interval between the energization ofthe cutoff relays 11 and 12 and the consequent deenergization of theslow releasing line relay 19, holding circuits for the cut-off relays11. and 12 are completed. The circuit for cut-of? relay 11 may bedescribed as extending from grounded battery, resistance 22, innerarmature and front contact of relay 19, conductors and 115, upperwinding, front contact and armature of relay 11 to ground. The circuitfor cut-oil relay 12 extends in multiple with the last directed circuitand may be traced from grounded battery, resistance 22, inner arn'iatureand front contact of relay 10, conductors 25 and 115, lower winding ofrelay 12, conductor .116, front contact and armature of relay 11 toground.

Since it has been assumed that the call ing line is of odd designation,the odd secondary line switch of Fig. 2 is now operated to select anidle bridge circuit. This is offected as soon as the relay 29 isoperated, since it completes an actuating circuit for the motor magnet30 from grounded battery, resistance, front contact and armature ofrelay 29, winding, armature and back contact of motor magnet 30, innerfront contact and armature of relay 29, back contact and armature ofrelay 27 to ground. Under the control of this circuit the odd secondary.line switch advances its brushes 31, 32, and 34- ,until its outgoingtest brush 31 encounters. an idle test terminal such as 35, whichcondition is indicated by the presence of ground potential on such testterminal. Let .it be assumed that the first bridge circuit tested by thetest brush 31 is busy, a condition which is indicated by the presence ofbattery potential on the test terminals such as 35 which is applied overtest conductors such as 36, through the innermost armature and frontcontact of relays such as 37. As long as the test brush 31 en counterstestterminals which are characterized by busy potential, the switchingrelay 27 will be included in the neutral branch of the Wheatstone bridgeso that it will. not be operated but the relay 29 remains operated andthe motor magnet 30 continues to advance the brushes of its line switch.lYhc1i,'howerer, the idle bridge circuit is reached by the test brush31, ground potential is applied through the innermost back contact andarmature of relay 37, over con ductor 36, to its terminal where thecircuit is completed through the te's brush 31, back contact andarmature of relay upper winding of relay 27, armature and front contactof relay 29 and through the resistance to grounded battery. The motormagllt) Lil

net 30 will be shunted by this circuit and will cease its operationWhile the relay 27 is operated and extends the connection thus farcompleted from the calling line through the front contacts and armatures26 and 28 to line switch brushes 33 and 34 from which the circuit iscompleted from brush 33, over conductor 39, inner continuity spring andback contact of relay 40, left hand Winding of relay 41 to ground andfrom grounded battery through the right hand winding of relay 41, backcontact and armature of relay 42, outer back contact and continuityspring of relay 40, conductor 43 to the line switch brush 34. Therelay'41 is energized in this circuit and at its front contact andarmature effects the operation of the slow releasing relay 37 whichmaintains the portion of the connection already completed. \Vith therelay 37 operated a. holding circuit is completed from grounded battery,resistance, innermost front contact and armature of relay 37, conductor36, test terminal 35, test brush 31, back contact and armature of relay33, through both windings in series of relay 27, its front contact 44and armature to ground.

It should be stated that the brushes 45, 46, .47, 48 and 49 of theregister selector are normally standing in engagement with the terminalsof this selector which are connected to an idle register sender so thatwhen the rela 37 is oaerated a circuit is completed for the relay 42starting from grounded battery, winding of the motor magnet 50, itsback'contact and armature, winding of relay 42, inner armature and backcontact of relay 51, back contact and continuity spring of trip relay52, right hand back contact and armature of ringing relay 53, middlecontact and armature of relay 37 to ground.

The relay 42 when energized, at its inner right hand armature opened theoperating circuit of the motor magnet 50 of the register selector and atits inner right hand front contact and armature closed a circuit fromground through brush 47, conductor 114, armature and back contact ofrelay 63, winding of sender holding relay 74 to grounded battery. Relay7 4 when operated closes a locking circuit for itself through itsarmature and contact. At the inner left hand armature and contact ofrelay 42 the impulse relay 54 appearing at the upper right hand cornerof Fig. 4 is included in the impulse circuit which extends from grmindedbattery, secondary winding of the induction coil, winding of relay 54,conductor 55, selector brush 46, front contact and armature of relay 42,outer back contact and continuity spring of relay 40, over conductor 43and the lower side of the calling line through the dial at the callingsubstation over the upper side of the calling line, conductor 39, innercontinuity spring and back contact of relay 40, left hand winding ofrelay 41 to ground. The relay 41 is thus maintained energized in thiscir cuit to keep the holding relay 37 operated. Also at this time thesource of dial tone indicated in the upper right hand corner of Fig. 4is inductively connected to the impulse circuit to transmit a tone tothe calling-subscriber to indicate that the circuit is in readiness toreceive the directive impulses from the dial sender at the callingsubstation. As soon as the relay 54 is energized it closes a circuitfrom ground, its left hand armature and front contact, conductor 56,tens register brush 57 in its normal position, armature back contact andwinding of the motor magnet 58 to grounded battery. This motor magnet isthus operated and advances the brushes 57 and 59 of the tens registerinto their second position, and this closes a circuit from ground, offnormal contacts 60, winding of the tens change-over relay 61, conductor62, winding of the relay 63 to grounded battery. The tens register isnoW in condition to receive directive impulses from the dial sendercorresponding to the tens digit of the wantednumber. Let it be assumedthat this digit is 2 and that the dial sender is therefore operated tosend two impulses. In response to the first'of these impulses, the relay54 retracts its armatures to close a circuit from ground, over conductor64, and register brush 57 in its second position, back contact, armatureand winding of the motor magnet 58, to grounded battery, which circuitadvances the units register brushes into their third position. At theclose of the first impulse the impulse relay attracts its armatures tocomplete a circuit extending from grounded battery, winding, backcontact and armature of the motor magnet 58, tens register brush 57 inits third position, inner front contact and armature of relay 61,conductor 65, right hand front contact and armature of impulse relay 54,conductor 66, off-normal contact 67 to ground. The tens register therebysteps its'brushes into their fourth position. At this time a multiplecircuit is closed for the change-over relay 61, extending from groundedbattery, winding of relay 63, conductor 62, winding of relay 61, olfnormal Contact 68, register brush 57, over the remainder of the circuitpreviously described as extending to ground, over conductors and 66. Inresponse to the second and last impulse of the tens series ofimpulses,'relay 54 again retracts its armature and closes a circuit fromground, off-normal contacts 67, conductor 66, right hand armature andback contact of relay 54, conductor 69, outer right hand front contactand armature of relay 61, register brush 57 in its fourth position,armature, back contact and. Winding of the impulse the impulse relaymotor magnet 58 to grounded battery. The motor magnet interrupts its owncircuit and advances its brushes one step into their fifth position. lfnen the impulse relay is again operated at the close of this series ofimpulses the motor magnet 58 advances the register brushes into theirsixth position over the circuit from grounded battery, winding of themotor magnet 58, back contact and armature of this magnet, registerbrush 57 in its fifth position, innermost front contact and armature ofrelay 61, conductor 65, front contact and armature of relay 54,conductor 66, off normal contact 67 to ground.

The change-over relay 61 which is slow releasing and which is heldenergized in multiple with the operating circuit of the motor n'iagnet58 now deenergizes to prepare an operating circuit for the motor magnetof the units register. The de-energization of the change-over relay 61closes a circuit which advances the units register into its secondposition. This circuit is from gronml-battery, winding, armature andback contact of the motor n'iagnet 70, units register brush 71,conductor '72, inner back contact and armature of relay 61, conducter65, front contact and armature of relay 54:, conductor 66, off normalcontacts 67 to ground. with the units register in its second position,the apparatus is in condition to receive the series of impulsescorresponding to-the units digit of the wanted number. Let it be assumedthat this units designation is 2, therefore the calling subscriberoperates his dial sender to transmit two impulses. In response to thefirst of these impulses the impulse relay 54 retracts its armature andthereby closes a circuit from ground, its left hand armature and backcontact, conductor 64:, register brush 71,

back contact, armature and winding of the motor magnet 70 to groundedbattery.

Under the control of this circuit the units register is advanced intoits third position. During this operation of the motor magnet the unitschange-over relay 73 is operated in a circuit in multiple of that forthe motor magnet which extends from grounded battery, winding of therelay 63, winding of the relay 7 through the remainder of the multiplecircuit extending through the register brush 71. At the close of thisfirst l attracts its armature to complete another operating circuit forthe motor magnet 70 from grounded battery, winding of this magnet, itsarmature and back contact, register brush 71, in its third position,conductor 72, inner hack contact and armature of relay 61, conductor 65,front contact and armature of relay 5a, conductor 66, off normalcontacts 67 to ground.

In response to the second and last impulse of this series of impulses,the impulse grounded battery, winding, armature and.

back contact of motor magnet 70, brush 71 in its fourth position,conductor 64%, back contactandarmature of relay 5% to ground. [it theclose of this impulse, the impulse relay 54 is again operated and theunit's register is moved into its sixth position in a circuit closedfrom grounded battery, winding of the motor magnet 70, its armature andback contact, register brush 71 in its fifth position, conductor 72 toground, over the remainder of the circuit previously described. Duringthe operation of the units register the slow releasing change-over relay73 has been held operated, but when the impulse relay at the close ofthe units series of impulses is held operated for a relatively longperiod, this change-over relay deenergizes to remove the tens and unitsregisters from any furthercontrol of the dial sender during this call.

[It will be ren'ienibered that the relay 74 is operated and closes alocking circuit for itself as soon as its register sender of Fig. 4 isseized, also at this time slow-releasing relay 75 is operated. If now,no other register sender of thegroup of lines under consideration ismaking a test the relay 77 is operated from grounded battery, winding ofthis relay, conductor 78 and its register brush 79 in its sixthposition, lowermost armature and back contact of relay 73, through bothwindings in series of relay 76, continuity spring 80 and back contact,back contact and continuity spring 81 of a relay 82 associated with asecond register sender, conductor 83, back contact and continuity spring84 to ground. The relays 76 and 77 are energized in this circuit andsince the relay 75 is slow releasing it will be held operatedmomentarily even though its circuit is now opened at the right hand backcontact and armature of relay 76. lVith relays 74, 75 and 76 operated. atest circuit is now completed from ground, inner armature and frontcontact of relay 74:, armature and front contact of relay 76, continuityspring and armature of relay 7 5, winding of relay 85, conductor 86,tens register brush 59, contact 87 and armature of relay 77, conductor88, inner armature and front contact of relay 12, primary line switchbrush 17, conductor 89, uppermost armature and back contact of relay 90,winding of relay 91, conductor 92, uppermost armature of multi-contactrelay 93 to grounded battery. The relays 91 and are operated in thiscircuit and the relay 85 closes a locking circuit for itself overconductor 86, winding of relay 85, its front contact and armature, backcontact and continuity spring of relay 75, front contact and armature ofrelay 76, front contact and armature of relay 74 to ground.

l/Vith relay 91 operated the terminating test brush 94 is renderedeffective and operates the slow releasing relay 95' in a circuit closedfrom grounded battery, winding of relay 95, front contact and armatureof relay 91 to ground. 7

With relay 95 operated, an actuating circuit for the motor magnet 96 iscompleted from grounded battery, resistance, lower front contact andarmature of relay 9 5, winding, armature and back contact of ,motormagnet 90, inner front contact and armature of relay 95, inner armatureand back contact of relay 90 to ground. the control of this circuit,motor magnet 90 advances the brushes 94, 97, 98 and 99 of the evensecondary line switch until the test brush 94 encounters the terminatingend of the bridge circuit to which the calling line has been extended.At this time, the switching relay 90 is operated in a circuit traceablefrom grounded battery, resistance, front contact and armature of relay95, lower winding of relay 90, armature and front contact of relay 91,terminating test brush 94, test terminal 1000f the bridge circuit whichhas been previously selected, conductor 101, register selector brush 45,conductor 1'02, upper front contact and armature of relay 85, to ground.The relay 90 is energized in this circuit and at its upper armature andcontact opens the circuit of relay 91. The relay 91 deenergizes andcompletes a circuit for the ringing relay 53 from grounded battery,winding of this relay, right hand back contact and continuity spring oftrip relay 52, outer left hand front contact and armature of relay- 37,conductor 103, terminal 104, brush 97. through both windings in seriesof relay 90, front contact and armature of this relay to ground. Therelay 90 is thus lock-ed operated and the ringing relay attracts itsarmatures to close a ringing circuit from the source of ringing currentGEN, right hand winding of trip relay 52, left hand armature and frontcontact of relay 53, COIHluctOl 106, even secondary line switch brush99, to the called substation, through the line switch brush 19, over thelower and upper sides of the called line, brush 18, through the upperside of the link circuit to brush 98, conductor 105, resistance 107,right hand front contact and armature of relay 53, middle front contactand armature of relay 37 to ground. Ringing current is applied over thiscircuit until the called party responds at which time trip relay 52 isenergized to efiect the dcenergization of the ringing relay 53, whichstops the ringing of the called station; also at this time alockingcircuitclosed for the trip relay 52, through the Under left hand windingof this relay, its armature and continuity'spring, right hand back turneffects the restoration of its register sender in the following manner:The release of relay 74 closes a circuit from grounded battery, winding,back contact and armature of motor magnet 58, off normal contact 68,conductor 108, lowermost back contact and armature of relay 74,conductor 109, off nor-' mal contacts 67 to ground. Under the control ofthis circuit the motor magnet 58 advances the brushes of the tensregister into their first or normal position. The units register isrestored by a circuit closed from grounded battery, winding of the motormagnet 70, conductor 110, off normal con tacts 111, inner back contactand armature of relay'74 to ground. Under the control of thiscircuit themotor magnet advances the brushes of the units register into their firstor normal position.

In the event that the called line is busy its test circuit previouslydescribed will not' be complete with the result that the relay is notenergized, the relay 51, will thereupon be operated in a circuittraceable from grounded battery, winding of this relay, its continuityspring and back contact, outer right hand front contact and armature ofrelay 42, brush 48, conductor 112, lower back contact and armature ofrelay 85, back contact and continuity spring of relay 75, right handfront contact and armature of relay 76, inner front contact and armatureof relay .74 to ground. The test relay 51 when thus operated closes alocking circuit for itself throughits continuity spring and armature,through the middle aanature and contact of relay 37 to ground.

At the termination of the connection when the calling subscriber at Areplaces his receiver on its switch hook, the relay 41 vole-- energizesand shortly afterwards slowreleasing relay 37 retracts its armature andthereby opens the holding'conductor 36 which has been maintaining therelay 27 en in its normal condition in readiness for the next call.

In the modified form of the invention shown in Fi 6, a commoninterrupter is provided for. operating the motor magnets of a group ofline switches. Prior to the use of such common interrupter it was foundin practice that where contacts are placed on each motor magnet by whichit interrupted its owncircuit such contacts were a. frequent. source oftrouble due to theinbeing out of adjustment.

WVhenthe subscriber at G removes-his receiverz fromits switch hook acircuit is closed for. the line relay 200 extending fromgroundedbattery, winding of this relay,

innen-upper armature andback contact of the line relay, conductor 205and resistance 213 to ground. Under the control of th1scircuit; themotormagnet advances its brushes-206, 207, and 208. of the line switch onestep forward.

This operation ofthe line switch closes-its oii-normalcontacts 209 and210 andopens the contacts 211. The closure of contacts 210 renders thecalling line busy and prevents itssei'zu're as a called line, while theclosure of contacts 209 completes a substitute operating, circuit forthe motor magnet extending. from ground, resistance 213, off nor malcontacts 209, winding of the motor mag-- net 202, lowermost back contactof the cutoff relay, conductor 204, common interrupter 203 to groundedbattery. Under the con trol of: this circuit the motormagnet advancesthebrushesof the line switch so that its test brush 208succcssivelyteststhe ter= minals of the trunks terminating in this switch.

Let it be. assumed that the first trunk tested isbusy, a conditionindicated by the presence of ground potential on its-test terminal 216,at which time the circuitcondition diagrammaticallyrepresented in Fig.8' exists. The test terminal 216 is at this time connected through aresistance 219 which corresponds to resistance 212 at the connector ofthe busy trunk to ground. Thistest terminal is also extended through atest brush similar to 208 of a-line switch which has previously seizedthis trunk and through a winding217 similarrto 218 ofthe cut-oii' relayassociated with that line switch and. through the innermost frontcontact and armature ofthis relay to grounded'battery. For this reasonwhen the brush 208 engages test terminal 216, the winding 21% of thecut-01f relay is included in the neutral branch of the l Jheatstonebridge represented by conductor 221. The. other side of the VVheatstonebridge extends from grounded battery, interrupter 203, conductor 204:,lowermost armature and back contact of the cut-off relay, winding of themotor magnet 202, 011' normalcontacts 209, resistance 213 to ground.Since the winding 214 of the cut-oil relay is at this time included inthe neutral branch of' the. VVheatstone bridge it will not be operated,but: the motor magnet will continue to operate in the last describedcircuit until the test brush 208 of the line switch encounters a testterminal such as 222 of an idle trunk; lVhcn such an idle trunk istested, the circuit condition diagrammatically represented in Fig.7exists. At this time a circuit is closed for the winding 214 of thecut-off relay extending from grounded battery, back contact andarmatureof relay 223, conductor 220, test terminal 222, test brush 208, winding21% of the cut-off relay, inner armature and front contact of line relay200, off normal contacts 209 resistance 213' to ground. The cut-offrelay is operated in this circuit but the motor magnet is shuntedthereby so that it does not advance the line switch further. As soon asthe cut-off relay is operated it extends the callingvline to the brushes200 and 207 of the line switch and through the windings 224i of theimpulse relay of the next switch in the connection to grounded battery.This relay is energized in the circuit and operates a slow releasingrelay 223, which extends a circuit from ground through resistance 212,front contact and armature of relay 223, conductor 220, test terminal222, test brush 208, lower winding 218, front contact and arma ture ofrelay 201 to grounded battery.

The operation of the next numerical switch in the series which is hereshown as a connector switch is'directively controlled from the dial atthe calling substation toextend the connection in the well known manner.

At the termination of the conversation when the calling subscriberreplaces his-receiver on its switch hook the impulse relay 224deenergizes and effects the d-eenergization of the slow releasing relay223, which removes the holding ground from the conductor 220 to effectthe 'deenergization of the cut-off relay 201. When this last named rclayretracts its armatures an operatingcircuit is closed for the motormagnet 202, extending from. ground, resistance 213, off normal contacts209, winding of the motor magnet 202, lowermost back contact andarmature o't the cut-oil relay 201, conductor 20%, interrupter 203 togrounded battery.

What is claimed is '1. In an automatic telephone system, a plurality oftelephone lines, a'plurality o'l trunks, a plurality of automaticswitches for interconnecting calling telephone lines and idle trunks,testing means associated with each automatic switch arranged to besuccessively extended to said trunks by the operation of its automaticswitch, and various resistances arranged to be connected with certain ofsaid testing means in the form or a \Wheatstone bridge during thetesting of busy trunks. V

2. In an automatic telephone system, a plurality of telephone lines, aplurality of trunks, automatic switches for interconnecting callingtelephone lines and idle trunks, .a cut-oil relay associated with eachautomatic switch, a line relay arranged to be operated over a telephoneline on the initiation of a call for starting the operation of anautomatic switch, a motor magnet for each automatic switch arranged tobe operated under the control of said line relay, said cut-off relayfunctioning to disable said line relay, a plurality of resistanceelements including said motor magnet, and means including an automaticswitch for arranging said resistance elements to form arms of a\Vheatstone bridge with said cut-off relay in the neutral branch of saidVVheatstone bridge circuit during the testing of a busy trunk and foroperating said cut-oli relay when an idle trunk is located.

3. In an automatic telephone system, a plurality of telephone lines, aplurality of trunks, each provided with a test conductor, automaticswitches for interconnecting lines and trunks, a battery, a motor magnetfor advancing each automatic switch, means controlled over the callingtelephone line for initiating the operation of a motor magnet to advanceits automatic switch, resistance units, a relay for disabling said motormagnet when an idle trunk is reached, said relay during the advance ofsaid switch having one of its terminals connected to opposite poles ofsaid battery through said motor magnet and a resistance unit, meansincluding said switch and the test conductor associated with a busytrunk for con necting the other terminal of said relay to the oppositepoles of said battery when said busy trunk is tested, whereby said relayis rendered inoperative, and means including the test circuit of an idletrunk having one of said resistance units in series to operate saidrelay when an idle trunk is located.

4. In an automatic telephone system, a plurality of telephone lines, aplurality of trunks, a plurality of line switches, each telephone linebeing connected to a line switch, a motor magnet for operating each lineswitch to extend its associated telephone line to an idle trunk, aplurality of resistance units, a relay for disabling said motor magnet,a test circuit completed during the testing of each busy trunk, saidcircuit having two branches connected in multiple, one branch includinga resistance unit and said motor magnet, said other branch including atleast two resistance units, said relay be ing connected at pointsbetween the resistance units of one branch and the resistance unit andthe motor magnet of the other branch, the resistance ofsaid resistanceunits and motor magnet being such that said relay is in a substantiallyneutral circuit, and means including one of said branches for operatingsaid relay when an idle trunk is located.

5. In an automatic telephone system, a

plurality of telephone lines, a plurality of trunks, a test conductorfor each trunk, an automatic switch to which each line is connected andby which said telephone line is extended to an idle trunk, one or. morebrushes for each line switch, means including a motor magnet operatingonthe initiation of a-call on a line for advancing its line switch tosuccessively engage the various trunks, a cut-ofi' relay for disablingits associated motor magnet when an idle trunk is located, an initialenergizing circuit for said outwit relay extending through a brush ofsaid line switch and the test conductor of an idle trunk to one terminalof said battery, and a holding circuit for said cut-off relay extendingthrough a second winding of said cut-oii relay, said line switch brush.and said conductor to theother pole of battery.

6. In an automatic telephonev system, a plurality of automatic switches,each provided with sets of movable contacts and fixed terminals, aplurality of pairs of telephone lines, each pair of telephone linesterminating in the movable contacts of an automatic switch, a pluralityof pairs of trunks multiply connected to the fixed terminals of aplurality of said switches, a test conductor for each pair of trunks,means including a motor magnet for advancing the movable contacts ofeach switch on the initiation of a call over one of its lines tosuccessively en.- gage the fixed contacts of the various pairs oftrunks, a battery, a cut-off relay for disabling said motor magnet whenan idle pair of trunks is located, an initial energizing circuit forsaid cut-ofi relay extending through a movable contact of said switchand the test conductor of an idle pair of trunks to one terminal of saidbattery, and a holding circuit for said cut-0E relay extending through asecond windingofsaid cut-off relay, said switch contact and saidconduetor to the other pole of battery.

7. In an auton'iatic telephone system, a; plurality of telephone lines,a plurality of trunks, automatic switches for inter-connecting callingtelephone lines and idlemotor magnet, said resistance units during thetesting of busy-trunks being included'by said automatic switches in alV-heatstone bridge arrangement, said cut-oil relays be ing includedin-the neutralbranch of said- Wheatstonc bridge during the testing orthe busy trunks and operating when an idle pair of trunks is located.

8. In an automatic telephone system, a plurality of telephone lines,aplurality oi trunks, a test conductor for each trunk, an automaticswitch to which each telephone line is-con-nected and by which saidtelephone line is extended to an idle trunk, one or more brushes foreach automatic switch, means including a motormagnet for advancing itsautomatic switch to successively engage the various trunks, a battery, acut-olt relay for disabling said motor magnet when an idle trunk islocated, said cut-oil relay being provided with two windings, an initialenergizing circuit for said cut-off relayextending through one winding,a brush or" said line switch and a test conductor of an idle'trunk toone terminal of said battery, and a holding circuit for saidcut-o'ifi-relay extending through the second winding of said cut-oilrelay, said line switch brush and said conductor to the other pole ofbattery.

9. In an automatic telephone system, a plurality of telephone linesarranged in pairs, a plurality of trunks, an automatic switch forinterconnecting apair o1 lines and a pair of trunks, a motor magnet foreach switch operating on the initiation of a call to advance said switchto an idle pair of trunks, a pair of cut-o'ii relays associated witheach pair of lines, contacts for each of said cut-oil relays eachtelephone line of a pair having its conductors controlled at contacts ofeach cut-otf' relay, each cut-oil relay serving to disable said motormagnet,- and means responsive to the interconnection of a pair oftelephone lines and a pair of trunks for operating the associatedcut-oft relays.

10'. In an automatic telephone system, a plurality of telephone linesarranged in pairs, a plurality of trunks arranged in pairs, a switch foreach pair of telephone magnet, the cut-oil relays function lines forextending the same to idle pairs of trunks, amotor magnet for advancingeach automatic switch past busy trunl-zs, a single line relay associatedwith and arranged to be operated over a pair of telephone lines tocontrol its motor magnet, a. pair of cut-oil relays associated with eachpair of telephone lines for disabling said line relay to stop said motormagnet, each of said cut-oil rclays controlling a break point in eachtelephone line of a pair, and means for encrgizing said cut-oft" relayswhen a pair of idle trunks are located.

11. In an automatic telephone system, a plurality of telephone lines, aplurality of trunks, test conductors associated with certain of saidtrunks, means including automatic switches for interconnecting saidtelephonelines with idle trunks, a motor magnet for each switch toadvance the same, a line relay associated with each motor magnet, saidline relay being operated on the initiation of a. czll over any one: ofseveral lines to start the operation of said motor magnet, a cut-offrelay for each telephone line, a circuit closed in series through eralof said cut-off relays over a condu tor of a trunk when the same isseized by an automatic switch, and a locking circuit for said cut-oilrelays including multiple cireuits also extending through said testconductor, said cut-oii relays on cue" zation serving to disable saidline relay and in turn the motor magnet of the automatic switch.

12. In an automatic telephone *stem, pairs of telephone lines, pairs oftrunks, an automatic switch for each pair of telephone lines forextending the same to idle pairs of trunks, a motor magnet for eachswitch for advancing the same, a single wound line relay for each pairof telephone lines serving when energized to cause the operation of itsassociated motor magnet, multiple operating circuits for each line relayinchidiug the two sides in series of each of the calling telephone linesof a pair, a cut-off relay for each telephone line of a pair, meansincluding said cut-ofi relays for disabling the associated line relay,and means for operating said cut-01f relays when an idle pair of trunksis located. v

13. In an automatic telephone system, a plurality of pairs of telephonelines, a, plurality of pairs of trunks, a switch individual to; eachpair of-telephone lines for extending the same to idle pairs of saidtrunks, means associated with each switch for advancing the same,testing means associated with each automatic switch arranged to besuccessively extended to said trunks by the operation oi its automaticswitch, and various resistances arranged-to be connected *ith saidtesting means in the form of a lVheatstone bridge during the testing ofbusy trunks.

1%. In an automatic telephone system, a

plurality of pairs of telephone lines, a plurality of pairs of trunks, aswitch individual to each pair of telephone lines for extending the sameto idle pairs of said trunks, means associated With each switch foradvancing the same, testing means associated with each automatic switcharranged to be successively extended to said trunks by the operation ofits automatic switch, various resistances arranged to be connected Withsaid testing 10 means in the form of a "Wheatstone bridge for testingthe busy or idle condition of the various pairs of trunks, andnon-numerical switching means for extending each trunk.

In witness whereof, I hereunto subscribe 15 my name this 1st day ofApril A. D. 1922.

' WINFRED T. POWELL.

